When I use notify-send to send a simple message to notification-daemon:
notify-send "hello"
it not only displays the message but also creates a system tray icon, as shown on the screenshot below:

This icon will stay in the system tray until I click on it and select "clear all notifications". This icon completely defeats the purpose of notify-send as unobtrusive notification. I have used notify-send few years ago and I am sure it did not have any tray icon back than. Needles to say, this is absolutely annoying.
I have found that I can use transient option
notify-send --hint=int:transient:1 hello
Which makes the icon disappear after a certain time. This is better, but still not acceptable.
Is there any way to get rid of the tray icon entirely?
I am using LXDE on Debian Wheezy
Some answers suggest, this is caused by my desktop environment (LXDE).
I find it hard to believe. I still suspect this is caused by notification daemon. I have downloaded sources for notification-daemon package, and there in the CHANGELOG I see, among other things:
- Added better support for attaching context notifications to an icon on the system tray, even when it moves. Patch by Colin Walters.
Which seems to be the "feature" that I am complaining about.
Can anybody advice how to disable systray notification in notification-daemon? When I grep the sources for tray or systray, I don't find anything. I don't know where to start.